Sly Defends Human Growth Hormone as Rambo Returns

Sylvester Stallone is back on the big screen playing a bulked-up Rambo in the fourth installment of the series – and isn't afraid to talk about what helped him get in fighting shape.

The 61-year-old star tells Time that he pumped up to 209 lbs. with the help of prescription testosterone.

"HGH [human growth hormone] is nothing. Anyone who calls it a steroid is grossly misinformed," he says. "Testosterone to me is so important for a sense of well-being when you get older. Everyone over 40 years old would be wise to investigate it because it increases the quality of your life."

Stallone also insists that others will see the light on HGH. "Mark my words. In 10 years it will be over the counter," he tells the magazine.

On Thursday, when the star turned up on the camouflage carpet for Rambo's Las Vegas premiere at the Planet Hollywood Resort and Casino, he did not speak about HGH, but focused on the perils of making the movie.

"There were a lot of death threats," Stallone told PEOPLE of filming along the Thailand/Burma border. "It was a very volatile, dangerous situation. We were filming in territory that was being controlled by some rough players and they didn't want any light shown on this dilemma, this civil war that's been going on for 60 years."

Stallone and the crew also endured insects, drastic weather changes and venomous snakes – which made this Rambo the most realistic one since the first installment in 1982, said Stallone.

His costar Julie Benz agreed that conditions were difficult. "It was a rough shoot... I had to get 17 vaccinations just to go do the movie."

Following the premiere, the film's stars moved to Prive Las Vegas for the afterparty.